Electric double layer capacitor and electrolytic cell

ABSTRACT

An electric double layer capacitor comprises: a cell which includes a pair of polarizable electrodes impregnated with an electrolytic solution and disposed in opposed relation with a separator interposed therebetween; collector electrodes respectively attached to the polarizable electrodes; and a sealing member of a synthetic resin which seals a periphery of the cell. The collector electrodes extend outward of the sealing member through the sealing member in contact with the sealing member. The collector electrodes each have a rough surface portion which extends through the sealing member.

TECHNICAL FIELD

The present invention relates to an electric double layer capacitor andan electrolytic battery.

BACKGROUND ART

Electric double layer capacitors are generally excellent incharge-discharge characteristics.

FIG. 17 is a sectional view of a cell 2 of a conventional electricdouble layer capacitor 1 (see Japanese Unexamined Patent Publication No.2001-351833). The cell includes a pair of polarizable electrodes 20, 21stacked with the intervention of a separator 6, and collector electrodes3, 30 of a metal are respectively attached to outer sides of thepolarizable electrodes 20, 21. The polarizable electrodes 20, 21 areprepared by adding an electrically conductive polymer such aspolypyrrole to powdery or fibrous active carbon, and compacting andpress-molding the active carbon together with a binder. The polarizableelectrodes 20, 21 are each impregnated with an electrolytic solutionsuch as of sulfuric acid. Not only an aqueous solution such as thesulfuric acid solution but also a nonaqueous solution to be describedlater is usable as the electrolytic solution.

Peripheral portions of the polarizable electrodes 20, 21 are sealed withan insulative sealing member 4 of a synthetic resin. The sealing member4 prevents the electrolytic solution from leaking out of the cell 2. Ingeneral, one or more such cells 2 are arranged laterally to constitutethe electric double layer capacitor 1.

When the cell is charged, a DC voltage is applied between the collectorelectrodes with one of the collector electrodes 3 being connected to apositive terminal of a power source and with the other collectorelectrode 30 being connected to a negative terminal of the power source.Anions are attracted to the polarizable electrode 20 connected to thepositive collector electrode 3, and cations are attracted to thepolarizable electrode 21 connected to the negative collector electrode30. Thus, an electric double layer structure is formed by thepolarizable electrodes 3, 30.

When the cell is discharged, the collector electrodes 3, 30 areelectrically connected to each other. Thus, electric charges accumulatedin the polarizable electrodes 20, 21 are discharged.

In the electric double layer capacitor, however, the adhesion betweenthe collector electrodes 3, 30 and the sealing member 4 is poor.Therefore, the electrolytic solution impregnated in the polarizableelectrodes 20, 21 is liable to leak from gaps between the collectorelectrodes 3, 30 and the sealing member 4, or moisture is liable tointrude into the inside of the sealing member 4 from the outside of thecell 2.

Particularly, the nonaqueous electrolytic solution is liable to beelectrolyzed in the cell 2 due to the intrusion of the moisture from theoutside, thereby deteriorating the characteristic properties of theelectric double layer capacitor.

It is an object of the present invention to provide an electric doublelayer capacitor and an electrolytic battery which are free from theleakage of the electrolytic solution and the intrusion of the moisturefrom the outside.

SUMMARY OF THE INVENTION

An electric double layer capacitor 1 comprises: a cell 2 which includesa pair of polarizable electrodes 20, 21 impregnated with an electrolyticsolution and disposed in opposed relation with a separator 6 interposedtherebetween; collector electrodes 3, 30 respectively attached to thepolarizable electrodes 20, 21; and a sealing member 4 of a syntheticresin which seals a periphery of the cell 2.

The collector electrodes 3, 30 extend outward of the sealing member 4through the sealing member 4 in contact with the sealing member 4.

The collector electrodes 3, 30 each have a rough surface portion 32which extends through the sealing member 4.

The rough surface portion 32 has a step 34 bent in the sealing member 4.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electric double layer capacitor;

FIG. 2 is a sectional view of an electric double layer capacitor havingsteps;

FIG. 3 is an exploded perspective view illustrating a production methodfor an electric double layer capacitor;

FIG. 4 is a plan view of a collector electrode and a second half body;

FIG. 5 is a sectional view of an electric double layer capacitor havingsteps;

FIGS. 6(a) to 6(d) are plan views of collector electrodes and secondhalf bodies;

FIG. 7 is a perspective view of a collector electrode having openings;

FIG. 8 is a perspective view of a collector electrode having slits;

FIG. 9 is a sectional view of an electric double layer capacitor havingsmall thickness portions;

FIG. 10 is a sectional view of an electric double layer capacitor havingresin layers;

FIG. 11 is a perspective view of a collector electrode formed with aresin layer;

FIG. 12 is a perspective view of a second half body employing thecollector electrode formed with the resin layer;

FIGS. 13(a) to 13(d) are sectional views of various examples of theresin layer;

FIG. 14 is a sectional view of an electric double layer capacitor havingsteps each formed with a resin layer;

FIG. 15 is a sectional view of an electric double layer capacitorincluding current collectors;

FIG. 16 is a plan view of a circuit board and an electric double layercapacitor; and

FIG. 17 is a sectional view of a conventional electric double layercapacitor.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described indetail with reference to the attached drawings.

Aqueous and Nonaqueous Electric Double Layer Capacitors First Embodiment

FIG. 1 is a sectional view of an electric double layer capacitor 1according to this embodiment. Like the conventional cell, a cell 2includes a pair of polarizable electrodes 20, 21 stacked with theintervention of a separator 6, and collector electrodes 3, 30 arerespectively attached to outer sides of the polarizable electrodes 20,21. The collector electrodes 3, 30 are metal plates of stainless steel,tungsten, aluminum or the like. In the following explanation, the upperpolarizable electrode 21 is defined as a negative electrode, and theupper polarizable electrode 20 is defined as a positive electrode.

A sealing member 4 includes first and second half bodies 40, 41 of arectangular prism shape each having a recess 42 formed in a centerportion thereof and vertically stacked with the recesses 42, 42 thereofcombined with each other. The polarizable electrodes 20, 21 and theseparator 6 are provided in the recesses 42, 42. The collectorelectrodes 3, 30 respectively extend outward through the correspondinghalf bodies 40, 41, and are bent along the side faces and the lowersurface of the sealing member 4.

The polarizable electrodes 20, 21 are each composed of powdery orfibrous active carbon, or a carbon nanomaterial such as fullerene orcarbon nanotube.

The first half body 40 and the second half body 41 are each formed ofglass, ceramic or a synthetic insulative resin. Examples of theinsulative resin include a modified polyamide, a nylon resin,polyethylene terephthalate, polypropylene and polyphenylene sulfide.

Examples of the electrolytic solution to be impregnated in thepolarizable electrodes 20, 21 include aqueous electrolytic solutionssuch as a sulfuric acid solution and a potassium hydroxide solution, andnonaqueous electrolytic solutions such as of triethylmethylammoniumtetrafluoroborate (Et₃MeNBF₄) and tetraethylammonium tetrafluoroborate(Et₄NBF₄) dissolved in aprotic organic solvents. Examples of the aproticorganic solvents include bifunctional solvents such as carbonates,lactones, nitrites, amides, nitroalkanes, sulfones, sulfoxides,phosphates, dinitriles and ethernitriles.

Usable as the separator 6 are nonwoven glass fabrics, pulp fabrics andfilms formed of insulative resins such as polytetrafluoroethylene(PTFE).

The negative collector electrode 3 includes a horizontal portion 31contacting the polarizable electrode 21, a rough surface portion 32connected to the horizontal portion 31 and extending through the firsthalf body 40, and an exposed portion 33 bent from the rough surfaceportion 32 along the first half body 40 and the second half body 41. Therough surface portion 32 intimately contacts the first half body 40.

Like the negative collector electrode 3, the positive collectorelectrode 30 includes a horizontal portion 31, a rough surface potion 32connected to the horizontal portion 31 and extending through the secondhalf body 41, and an exposed potion 33. The rough surface portions 32are each formed by a surface roughening treatment, and have an averageroughness of not smaller than 0.3 μm along a center line thereof. Thesurface roughening treatment may be achieved by etching, sandblasting,knurl, sand paper or the like.

The provision of the rough surface portions 32 which extend through thesealing member 4 increases the adhesion between the sealing member 4 andthe collector electrodes 3, 30. Further, contact surface areas of thecollector electrodes 3, 30 and the sealing member 4 are increased. Thisprevents the leakage of the electrolytic solution from the inside of thesealing member 4 and the intrusion of the moisture from the outside ofthe sealing member 4.

Another conceivable arrangement for effectively preventing the leakageof the electrolytic solution and the intrusion of the moisture form theoutside of the cell 2 is shown in FIG. 2. In this arrangement, the roughsurface portions 32 each have a step 34 bent as having two stages.

With the provision of the steps 34, the rough surface portions 32 eachhave an increased length as compared with the straight rough surfaceportions 32. Thus, the length of a path along which the moistureintrudes into the cell 2 from the outside of the sealing member 4, ifany, is increased, so that the leakage of the electrolytic solution andthe intrusion of the moisture from the outside are further assuredlyprevented. Where the rough surface portions 32 are bent, the collectorelectrodes 3, 30 are prevented from displacing in the first half body 40and the second half body 41 when the collector electrodes 3, 30 are bentalong the outer surfaces of the sealing member 4. This stabilizes thecharacteristic properties of the electric double layer capacitor 1, andimproves the yield of the electric double layer capacitor 1.

Production Method for Electric Double Layer Capacitor

The cell 2 of the electric double layer capacitor 1 shown in FIG. 1 isconstructed as illustrated in FIG. 3. The first half body 40 is preparedby insert-molding with the negative collector electrode 3 insertedtherein. The recess (not shown) of the first half body 40 opensdownward. Similarly, the second half body 41 is prepared byinsert-molding with the positive collection electrode 30 insertedtherein. The recess 42 of the second half body 41 opens upward.

The pair of polarizable electrodes 20, 21 are disposed in the recesses42 of the half bodies 40, 41 with the separator 6 interposedtherebetween. The separator 6 and the polarizable electrodes 20, 21 arepreliminarily impregnated with the electrolytic solution by vacuumfilling. After the half bodies 40, 41 are combined with each other, theperipheral edges of the half bodies 40, 41 are bonded to each other byultrasonic welding or the like. Thereafter, the exposed portions 33 ofthe collector electrodes 3, 30 are bent downward along the peripheralsurfaces of the half bodies 40, 41. Thus, the electric double layercapacitor 1 shown in FIG. 1 is completed.

Second Embodiment

This embodiment is characterized in that the collector electrodes 3, 30each have a resin filling portion 5. FIG. 4 is a plan view of thecollector electrode 30 and the second half body 41 in this embodiment.More specifically, the collector electrode 30 has round openings 50, 50formed therein as the resin filling portion 5 to be filled with a resinof the second half body 41. By filling the openings 50, 50 with theresin, the adhesion between the collector electrode 30 and the secondhalf body 41 is increased. As indicated by an arrow X in FIG. 4, thelength of a path along which the electrolytic solution flows out of therecesses 42 to the outside of the sealing member 4, if any, is increasedbecause the electrolytic solution flows along the peripheral edges ofthe openings 50. This prevents the leakage of the electrolytic solutionfrom the inside of the sealing member 4 and the intrusion of themoisture from the outside of the sealing member 4. Of course, the othercollector electrode 3 may also have openings 50, 50.

The resin filling portion 5 may be provided in the form of slits 51 or amesh 52 formed in the collector electrode 30 as shown in FIGS. 6(a) to6(c). The formation of the slits 51 and the mesh 52 may be achieved bystamping. As shown in FIG. 6(d), the resin filling portion 5 may haveslits 51 and a mesh 52 in combination.

Further, as shown in FIG. 5, the collector electrodes 3, 30 may each bebent into a two-stage step 34 which includes a horizontal plate portion34 a and a vertical plate portion 34 b, and the resin filling portion 5may be provided in the step 34. FIGS. 7 and 8 are perspective views ofcollector electrodes 3 each having such a step 34. The resin fillingportion 5 may include openings 50 or slits 51.

In FIG. 7, openings 50 formed in the horizontal plate portion 34 a ofthe step 34 and openings 50 formed in the vertical plate portion 34 bare located in laterally staggered relation. More specifically, theopenings 50 of the horizontal plate portion 34 a are located belowspaces between the openings 50, 50 of the vertical plate portion 34 b.Thus, even if the electrolytic solution leaks from the peripheral edgesof the openings 50 of the vertical plate portion 34 b, the electrolyticsolution flows along the peripheral edges of the openings 50 asindicated by an arrow X1 in FIG. 7. Even if the electrolytic solutionleaks through the spaces between the openings 50, 50 of the verticalplate portion 34 b as indicated by an arrow X2, the electrolyticsolution flows along the peripheral edges of the openings 50 of thehorizontal plate portion 34 a. As a result, the length of a path alongwhich the electrolytic solution flows out of the sealing member 4, ifany, is increased, thereby preventing the leakage of the electrolyticsolution and the intrusion of the moisture from the outside of thesealing member 4. Further, as shown in FIG. 8, slits 51 formed in thehorizontal plate portion 34 a and slits 51 formed in the vertical plateportion 34 b may be located in laterally staggered relation.

Further, as shown in FIG. 9, the collector electrodes 3, 30 may eachhave a small thickness portion 35 having a thin cross section in contactwith the half body 40, 41. In this case, a space above the smallthickness portion 35 is filled with the resin of the sealing member 4,so that the small thickness portion 35 serves as the resin fillingpotion 5. With the provision of the small thickness portion 35, thecontact surface areas of the collector electrodes 3, 30 and the sealingmember 4 are reduced. This prevents the leakage of the electrolyticsolution and the intrusion of the moisture from the outside of thesealing member 4.

Third Embodiment

This embodiment is characterized in that resin layers 8 are provided onthe collector electrodes 3, 30, and the collector electrodes 3, 30 arebonded to the sealing member 4 with the intervention of the resin layers8. FIG. 10 is a sectional view of an electric double layer capacitor 1according to this embodiment. The resin layers 8 are composed of amaterial which is more adhesive to the collector electrodes 3, 30 thanthe material for the sealing member 4. More specifically, where thesealing member 4 is composed of a liquid crystal polymer orpolypropylene, the resin layers 8 are composed of an epoxy resin. Theprovision of the resin layers 8 increases the adhesion between thecollector electrodes 3, 30 and the sealing member 4. This prevents theleakage of the electrolytic solution from the inside of the sealingmember 4 and the intrusion of the moisture from the outside of thesealing member 4.

As shown in FIGS. 13(a) to 13(d), the resin layers 8 protrude out of thesealing member 4 or into the recess 42. In order to ensure properadhesion between the sealing member 4 and the collector electrodes 3,30, the width of the resin layers 8 should be at least about 70% of thewidth L1 of portions of the collector electrodes 3, 30 contacting sideportions of the sealing member 4.

The resin layers 8 preferably each have a thickness of not greater than100 μm and not smaller than 1 μm. If the resin layers 8 are too thin ortoo thick, the strength of the bonding between the collector electrodes3, 30 and the sealing member 4 is reduced. Further, where the resinlayers 8 are composed of a resin having a higher water absorption factorthan the resin of the sealing member 4 and have an excessively greatthickness, moisture in the resin layers 8 is liable to migrate into thesealing member 4. Therefore, the thickness of the resin layers 8 isspecified as described above.

Production Method for Electric Double Layer Capacitor

The electric double layer capacitor 1 according to this embodiment isproduced in the following manner.

As shown in FIG. 11, a liquid epoxy resin is applied transversely of thecollector electrode 30 on front and back surfaces of the collectorelectrode 30 for formation of the resin layer 8. After the epoxy resinis dried, the second half body 41 is prepared by insert-molding with thecollector electrode 30 inserted therein as shown in FIG. 12. The resinlayer 8 is positioned in a side portion of the second half body 41. Thefirst half body 40 is prepared in the same manner as described above.The separator 6 and the polarizable electrodes 20, 21 are placed in thehalf bodies 40, 41, which are combined with each other. Thus, theelectric double layer capacitor 1 is produced. As shown in FIG. 14,portions of the collector electrodes 3, 30 to be embedded in the sideportions of the sealing member 4 may be each formed with the steps 34,and the resin layers 8 may be formed on the steps 34.

Further, as shown in FIG. 15, current collectors 85, 85 may berespectively provided between the polarizable electrodes 20, 21 and thecorresponding collector electrodes 30, 3. The resin layers 8 areprovided on the portions of the collector electrodes 30, 3 to beembedded in the side portions of the sealing member 4. The currentcollectors 85, 85 are composed of a metal different from the materialfor the collector electrodes 3, 30. More specifically, the collectorelectrodes 3, 30 are composed of copper or nickel, while the currentcollectors 85, 85 are composed of stainless steel, aluminum, tungsten orthe like. The current collectors 85, 85 are formed by applying metalfoils on the collector electrodes 3, 30 or plasma-spraying the currentcollector material on the collector electrodes 3, 30.

Aqueous or Nonaqueous Electrolytic Battery

The present invention is applicable to an aqueous or nonaqueouselectrolytic battery.

The electrolytic battery has substantially the same construction and isproduced in substantially the same manner as the electric double layercapacitor, except that some of its components are composed of differentmaterials.

In the case of the nonaqueous electrolytic battery, the polarizableelectrodes of the electric double layer capacitor are replaced with apositive active material member and a negative active material member.The positive active material member is prepared by press-molding orsintering powder of lithium cobaltate, lithium manganate, lithiumnickelate or the like. The negative active material member is preparedby press-molding or sintering powder of graphite carbon material or cokecarbon material.

A solution of a lithium salt dissolved in an organic solvent is used asthe electrolytic solution. Examples of the lithium salt include LiBF₄,LiClO₄, LiPF₆, LiASF₆, Li(CF₃O₂)₂N and LiC₄F₉SO₃. Examples of theorganic solvent include propylene carbonate, γ-butyrolactone and amixture of propylene carbonate or γ-butyrolactone and a chain carbonate.Examples of the chain carbonate include dimethyl carbonate (DMC, DEC)and ethyl methyl carbonate (EMC).

A porous polymer film such as of polyethylene, polypropylene or a likepolyolefin is used as the separator. A positive collector electrode 30is composed of aluminum or the like, and a negative collector electrode3 is composed of copper.

In the case of the aqueous electrolytic battery such as alithium ionbattery, the positive active material member is prepared by sintering orcompact-molding powder or a pellet of nickel oxide, and the negativeactive material member is prepared by sintering or compact-moldingpowder or a pellet of an Mm—Ni—Co—Mn—Al hydrogen-absorbing alloy(wherein Mm is a mixture of a rare earth element).

A solution of potassium hydroxide or a polymeric hydrogel electrolyte isused as the electrolytic solution. A porous polymer film such as of asulfonated polypropylene is used as the separator.

In general, the electric double layer capacitor and the electrolyticbattery each have a rectangular prism shape or a disk shape. However,where the electric double layer capacitor or the electrolytic batteryhaving a disk shape is mounted on a circuit board 7 as indicated byhatching in FIG. 16, there is a dead space 70. Therefore, therectangular prism shape is preferred for effective utilization of asurface area of the circuit board 7.

INDUSTRIAL APPLICABILITY

In the inventive electric double layer capacitor 1, the collectorelectrodes each have the rough surface portion 32 which extends throughthe sealing member 4. Therefore, the adhesion between the sealing member4 and the collector electrodes 3, 30 is improved. Further, the contactsurface areas of the sealing member 4 and the collector electrodes 3, 30are increased. This prevents the leakage of the electrolytic solutionfrom the inside of the sealing member 4 and the intrusion of themoisture from the outside of the sealing member 4.

Further, the rough surface portion 32 having the step 34 has anincreased length as compared with the straight rough surface portion 32.Therefore, the length of the path along which the moisture intrudes intothe cell 2 from the outside of the sealing member 4, if any, isincreased, so that the leakage of the electrolytic solution and theintrusion of the moisture from the outside can be further assuredlyprevented. Where the rough surface portions 32 are bent, the collectorelectrodes 3, 30 are prevented from displacing in the first half body 40and the second half body 41 when the collector electrodes 3, 30 are bentalong the outer surfaces of the sealing member 4. This stabilizes thecharacteristic properties of the electric double layer capacitor 1, andimproves the yield of the electric double layer capacitor.

1. An electric double layer capacitor comprising: a cell which includesa pair of polarizable electrodes impregnated with an electrolyticsolution and disposed in opposed relation with a separator interposedtherebetween; collector electrodes respectively attached to thepolarizable electrodes; and a sealing member of a synthetic resin whichseals a periphery of the cell, wherein the collector electrodes extendoutward of the sealing member through the sealing member in contact withthe sealing member, wherein the collector electrodes each have a roughsurface portion which extends through the sealing member.
 2. An electricdouble layer capacitor as set forth in claim 1, wherein the roughsurface portion has a step bent in the sealing member.
 3. An electricdouble layer capacitor comprising: a cell which includes a pair ofpolarizable electrodes impregnated with an electrolytic solution anddisposed in opposed relation with a separator interposed therebetween;collector electrodes respectively attached to the polarizableelectrodes; and a sealing member of a synthetic resin which seals aperiphery of the cell, the sealing member including two half bodiescombined with each other and respectively having recesses in which thecell is fitted, wherein the collector electrodes each have a resinfilling portion located on a lateral side of the recess and filled withthe resin of the sealing member.
 4. An electric double layer capacitoras set forth in claim 3, wherein the collector electrodes each have astep bent in the sealing member.
 5. An electric double layer capacitoras set forth in claim 3, wherein the resin filling portion has at leastone of an opening, a slit, a mesh and a small thickness portion.
 6. Anelectric double layer capacitor comprising: a cell which includes a pairof polarizable electrodes impregnated with an electrolytic solution anddisposed in opposed relation with a separator interposed therebetween;collector electrodes respectively attached to the polarizableelectrodes; and a sealing member of a synthetic resin which seals aperiphery of the cell, wherein the collector electrodes extend outwardof the sealing member through the sealing member in contact with thesealing member, wherein the collector electrodes are each provided witha resin layer, and bonded to the sealing member with the intervention ofthe resin layer.
 7. An electric double layer capacitor as set forth inclaim 6, wherein current collectors are provided between the polarizableelectrodes and the corresponding collector electrodes.
 8. Anelectrolytic battery comprising: a cell which includes a pair of activematerial members impregnated with an electrolytic solution and disposedin opposed relation with a separator interposed therebetween; collectorelectrodes respectively attached to the active material members; and asealing member of a synthetic resin which seals a periphery of the cell,wherein the collector electrodes extend outward of the sealing memberthrough the sealing member in contact with the sealing member, whereinthe collector electrodes each have a rough surface portion which extendsthrough the sealing member.